My U.S. Pat. No. 5,279,716, "Method for Producing Magnesium Metal from Magnesium Oxide," discloses a practice for utilizing low cost magnesium oxide as a feedstock for an electrolytic process in which a substantially chloride-based salt bath including a rare earth chloride was used as the electrolyte. That process offers the opportunity to substantially reduce the cost of producing magnesium metal because it enables the use of magnesium oxide or a suitable precursor as a feedstock material.
I have now discovered a process that utilizes a fluoride salt electrolyte that offers advantages over my chloride electrolyte process. I have found fluoride electrolyte compositions that provide a broader electrical potential range for magnesium oxide electrolysis without decomposing any of the fluorides in the electrolytes. They also provide higher ionic conductivity, greater capacity for magnesium oxide dissolution and faster rates of magnesium oxide dissolution. Furthermore, my fluoride electrolyte practice provides a method of preparing inexpensive, high quality magnesium-rare earth alloys (such as, for example, magnesium-neodymium alloys) ranging from practically pure magnesium to about 15 weight percent neodymium.